1. Field of the Invention
Embodiments of the present invention relate to ultrasound imaging probes, and particularly, to flexible, single chip, CMUT based ultrasound imaging probes using monolithically integrated CMUT arrays on CMOS electronics.
2. Background of Related Art
Side-looking intravascular ultrasound (“IVUS”) imaging probes exist that provide relatively high resolution images of tissue and fluid. This can be useful, for example, when inspecting the inside surfaces of vessels or tissues immediately surrounding the vessel. Similarly, intracardiac echocardiography (“ICE”) probes also exist which use one-dimensional (1-D) imaging arrays.
Unfortunately, current commercial IVUS imaging systems offer only side-looking capabilities and cannot generate images of, for example, the volume in front of the catheter. ICE probes, for example, provide only two-dimensional cross sections, but not volumetric images. The ability to image fluid and/or tissue directly in front of the probe can be useful in a number of applications. An IVUS catheter that can provide forward-looking volumetric ultrasound images would be a valuable clinical tool for, for example and not limitation, guiding interventions in coronary arteries, for the treatment of chronic total, or near-total, vascular occlusions, and for stent deployment.
In order to navigate tortuous arteries and coronary structures, for example, an important aspect of IVUS and ICE probes is the size and flexibility of the probes. As a result, the rigid section of the probe close to the imaging tip should be as short as possible. Current ultrasound array probes used for these purposes are rigid over several mm, limiting their maneuverability.
Similarly, for flexibility, the number of electrical connections connecting the probe to the back end imaging system should also be limited. In other words, a larger number of cables make the catheter less flexible. The number of external connections is also important, for example, because excessive external connections increase probe size and manufacturing cost and complexity.
In addition, to enable the probe to enter small areas (e.g., blood vessels), for example, the frontal area of the probe must be limited. To obtain the better resolution given the limited area of the probe, however, the array elements are preferably placed around the periphery of the frontal probe area. Furthermore, if possible, the transmit and receive array elements should be separate to achieve high signal to noise ratio. This is because when the same element is used for both transmit and receive functions some protection circuitry needs to be implemented, increasing the electronics noise of the system.
As a result, forward-looking, highly flexible IVUS probes that would generate full volumetric images in front of the catheter have not been feasible using conventional technology. There are IVUS catheters that use a single rotating transducer angled from the normal from the vessel wall, but these provide images only on a conical surface, not the 3-D volume.
In addition to size and flexibility constraints, ultrasound probes typically must limit their power consumption When the probe is activated, the temperature of the probe must be limited to prevent damage to tissue, or simply to prevent the probe from overheating when in open air. In some instances, for example, the probe may remain active outside the body. In this instance, power consumption should be limited to prevent the probe electronics from overheating and damaging the mechanical structure of the probe such as the adhesion layers.
What is needed, therefore, is a single chip, flexible, forward-looking ultrasonic probe. The probe should comprise reduced power consumption through electronics design and intelligent power control. The probe should comprise improved resolution with minimal cross-sectional area. The probe should comprise temperature feedback and control. It is to such an ultrasonic probe that embodiments of the present invention are primarily directed.